Polyvinyl acetal resins



Patented June 13, 1939 UNITED STATES PATENT OFFICE.

POLYVINYL AOETA L RESINS Harold F. Robertson, Coraopolis, Pa., assignorto Carbide and Carbon Chemicals Corporation, a corporation of New YorkNo Drawing. Application April 1, 1939, Serial No. 265,515

6 Claims.

This invention is directed to a group of artificial resinous substanceswhich are capable of being formed into plastic compositions havingremarkable properties of flexibility and resiliency coupled with greatstrength and toughness. The invention is specifically concerned withcertain novel members of the general class termed polyvinyl acetalresins.

It is known that polyvinyl alcohol (obtainable 'by the saponification orhydrolysis of such polymerized vinyl esters as polyvinyl acetate) is awater-soluble substance which can be reacted with aldehydes to formresinous materials. Most of these materials previously disclosed in theart are thermoplastic, and difier from polyvinyl alcohol itself in thatthey are not soluble in water, but are soluble in a wide variety oforganic substances, including many water-insoluble solvents, such asaromatic hydrocarbons, chlorinated hydrocarbons and various esters. Asin the case of the simple alcohols, polyvinyl alcohol combines withaldehydes in the proportion of two molecular equivalents of itstheoretical monomer, vinyl alcohol, to each molecular equivalent ofaldehyde. Because these reaction products are analogous to thealkylidene diethers, they are usually called polyvinyl acetal resins.Two related mem-- bers of the polyvinyl acetal class also are known. Oneincludes the substances formed by the re- I polyvinyl esters, and theseresins. contain principally ester and acetal groups in their molecule.Such substances may be termed polyvinyl acetalester resins, and they areintermediate, in 'general properties and solubility characteristics,between the polyvinyl acetals and the polyvinyl esters. The other typeof product may be'termed polyvinyl alcohol-acetals, and are formed bythe reaction of aldehydes with polyvinyl alcohol to an extentinsuflicient to render the porduct soluble in water-insoluble esters andthe like, and thus are closely related to polyvinyl alcohol'itself.

Polyvinylesters, polyvinyl alcohol, the polyvinyl acetal resins,polyvinyl acetal-ester resins, and the polyvinyl alcohol-acetalsreferred to, may each form the basis of film-forming or plasticcompositions. In general, these resins may be softened, or plasticized,to increase their flexibility by means of the solvents in which they'aresoluble. Thus, polyvinyl esters, polyvinyl acetals and polyvinylester-acetal resins may be softened by the addition of high-boilingesters (which are solvents for these materials), and polyvinyl al- Icohol and the polyvinyl alcohol-acetals may be action of aldehydes withpartially hydrolyzed solvent for polyvinyl alcoholll In the latter case,the volatility of water and its consequent tendency to be lost from thecompositions can be partially offset by the use of hygroscopic agents,such as glycerine, in the compositions. This expedient has been proposedas particularly fruitful in the case of the polyvinyl alcohol-acetals,which, even when not soluble in water, are highly water-absorptive andare rendered soft and flexible by water, with or without addedglycerine. The polyvinyl alcohol-acetals which are not soluble in waterare usually soluble .in the lower aliphatic alcohols and may beplasticized and rendered extensible by means of such solvents. Theflexibility of these compositions almost invariably increases with andin direct proportion to the quantity of solvent plasticizem added. Whenthe plasticlzed compositions are subjected to tensile tests and theelongation observed as a function of the load applied, it will be seenthat, as the amount of solvent'plasticizer in the composition isincreased, the load required to produce a given elongation is markedlydecreased.

Because of this fact, the resins discussed, when suflicientlyplasticized to have high flexibility and extensibility, yieldcompositions of greatly reduced ultimate strength as compared with theunplasticized material. In addition, such compositions lack elasticity;that is, while they are flexible, they do not recover their originaldimensions after the load applied is removed; 'The properties ofcompositions of these resins cannot be improved by attempting to softenthe water-soluble polyvinyl alcohol or the polyvinyl alcohol-acetalswith non-solvent plasticizers, such as the high-boiling esters, or byattempting to plasticize the ester-soluble polyvinyl esters, polyvinylacetals, or the polyvinyl ester-acetals with water, owing to thecomplete lack of compatibility of the ingredients of such systems. Thus,where flexible and highly extensible compositions of the resinsdiscussed are required, it is necessary to soften the resins withplacticizers that are also solvents for the resins, with the inevitableresult that products of low ultimate strength are secured which arealmost entirely without elasticity. In addition, the polyvinyl esters,polyvinyl acetals and polyvinyl acetal- -esters, when softened withsolventplacticizers, are softened by heat at temperaturesmuch below theheat softening temperatures of the unplacticized material, whilepolyvinyl alcohol and polyvinyl alcohol-acetals, when softened by wateror water-soluble agents, have been found to be clarity and adhesivenesswhich have lasting properties of flexibility, resilience and elasticity,coupled with great strength and toughness. The invention also includesplasticized compositions of the new resins, and the methods of makingthese resins.

The new resins of my invention differ from the polyvinyl ester,polyvinyl acetal, and polyvinyl acetal-ester resins in that they havestrikingly different and totally unexpected elastic properties whenplacticized with water-soluble ester plasticizers, and they differ fromthe known polyvinyl alcohol-acetal resins (and, of course, frompolyvinyl alcohol) in that they may be plasticized with water-insolubleester plasticizers to yield homogenous and elastic compositions of highultimate strength that have good adhesion to smooth surfaces.

The new resins which enable the objects of the invention to be achievedmay be classed as polyvinyl alcohol-acetal resins, or polyvinyl partialacetal resins, of a very definite composition, and the composition ofthese particular resins was not at all predictable from a study of knownresins of related types. The new resins are made by the reaction ofcertain aldehydes with polyvinyl alcohol or polyvinyl esters, and, ingeneral, to obtain materials of adequate strength, the polymeric vinylcompound from which they are formed should have an averagemacromolecular weight of at least 7,000. Resins made according to thisinvention from polyvinyl bodies having average molecular weights inexcess of 25,000 yield plasticized compositions of exceptionally hightensile strength and are the preferred resins of my invention.(Molecular weights referred to herein are calculated by means ofStaudingers formula from viscosity determinations on solutions of thematerials.)

The resins contemplated by this invention are limited both by the natureand the quantity of the aldehyde contained in them, and these resinscontain substantially only free hydroxyl groups of polyvinyl alcohol andacetal groups in their molecule. The proportion of aldehyde or acetal inthe new resins will be indicated throughout as percent acetalization(which indicates the percentage of hydroxyl or functional groups in thepolymeric body that are combined with aldehyde) and it is to beunderstood that my new resins are free from ester groups or any othergroups in amounts sufficient to affect the solubility or othercharacteristics of the materials.

The aldehydes from which my new resins are made are butyraldehyde,propionaldehyde and valeraldehyde, and the order of preference amongthese three aldehydes is that given. The extent of acetalization for mynew resins is different for each aldehyde. In any case, the degree ofacetalization with the aldehyde material containing at least one of thesaturated aliphatic aldehydes having from 3 -to 5 carbon atoms in itsmolecule must be so correlated with the kind of aldehyde and the freehydroxyl groups in the resin that the product has those propertiescharacterizing the resins of this invention. Thus, with butyraldehyde,the resins must be acetalized between about 54% and about 78%; withpropionaldehyde, between about 62% and about 88%; and, withvaleraldehyde, between about 39% and about 58%. These differences areoccasioned by the fact that the properties of the resins have been foundto vary with the length of the hydrocarbon chain of the aldehyde used,and the degrees of acetalization recited above have been found by testto be those which delimit resins of substantially the same properties.

This application is directed specifically to those resins made frompropionaldehyde, and resins made from butyraldehyde and fromvaleraldehyde are the subjects of my copending applications Serial Nos.236,556, filed October 22, 1938 and 265,516 filed April 1, 1939,respectively.

I have tried to make resins equivalent to those just. defined usingother aldehydes, but, so far as I have been able to determine, resinswhich are fully the equivalent of those of this invention with respectto color, strength or solubility characteristics cannot be formed fromaldehydes of less than three or more than five carbon atoms regardlessof their degrees of acetalization. Thus, certain of the desiredqualities of the new resins may be obtained in resins made fromacetalclehyde within certain narrow limits of acetalization, and certainother of the desired characteristics may be provided in resinsacetalized with hexaldehyde within certain other narrow limits, but inno case have I found it possible to make resins from either of these twoaldehydes which have all, or nearly all, of the outstanding propertiesof the resins specified above. Using formaldehyde alone or aldehydeshigher than hexaldehyde, it is, so far as I have ascertained, notpossible .to make resins which have the qualities of the resins of thisinvention to any significant extent.

The resins of this invention are not soluble in water, but, unlike thepolyvinyl ester, polyvinyl acetal and polyvinyl acetal-ester resinspreviously known, they are also, in general, not soluble inwater-insoluble organic solvents at ordinary temperatures. (The termordinary temperatures" as used herein refers to temperatures below 400.; usually C., or lower). Similarly, they are not dissolved at ordinarytemperatures by ester plasticizers, although the new resins themselveshave the unusual property of absorbing or dissolving sufficientquantities of ester plasticizers to yield adequately softened,homogeneous compositions. For example, the new resins at ordinarytemperatures are generally insoluble in such organic liquids asaliphatic and aromatic hydrocarbons; in ketones; in chlorinatedhydroparbons, including ethylene dichloride, methylene chloride andchloroform; or in esters, such as ethyl acetate, diethyl phthalate andpolyethylene glycol hexoates. Portions of the more highly acetalizedresins of this invention may dissolve in certain of the chlorinatedhydrocarbons or in certain of the ketones, but this partial solubilityin the ketones and chlorinated hydrocarbons in no way indicates thatsuch resins are beyond the scope of this invention or are lacking in thenew properties which characterize the resins of this invention. Theseresins are, in general, soluble in water-soluble liquids, such as thealco hols, glycol monoalkyl ethers and the like. In any case, the mostoutstanding characteristic of the new resins is their virtualinsolubility in water-insoluble ester plasticizers at ordinarytemperatures, coupled with the capacity of the resins themselves toabsorb suflicient quantities of these readily softened by plasticizersto give homogeneous compositions which have high extensibility andelasticity while retaining a high ultimate strength. The new resins (andtheir plasticized compositions) are thermoplastic in nature, althoughthey are less heat than many of the polyvinyl ester, polyvinyl acetaland polyvinyl acetalester resins previously known. Their heat softeningtemperatures, in general, are inversely proportional both to the degreeof acetalization and to the number of carbon atoms in the aldehyde usedin the formation of the resins.

Plastic compositions having high flexibility coupled with high ultimatestrength are of ex-. treme importance for such specialized uses as theinner layers for laminated safety glass, where it is desirable to use amaterial having high flexibility in order to absorb the force of a blowover considerable displacement. It is also very desirable that theplastic have a high ultimate strength coupled with flexibility in orderthat an object striking the laminated glass will be restrained fromcontinuing through it after its velocity has been reduced by theyielding inner layer. These desirable properties cannot be obtained inplastic compositions made from the known polyvinyl ester, polyvinylacetal, polyvinyl acetal-ester, polyvinyl alcohol, or polyvinylalcohol-acetal resins when rendered flexible by means of solventplasticizers because, as pointed out above, the ultimate strength ofsuch compositions is reduced greatly when these materials are madeflexible by such plasticizers. In general, plastic compositions havinghigh flexibility and elasticity and high ultimate strength may bedefined as those which have an elongation, when subjected to tensiletests at ordinary temperatures, of at least about 200% and which do notfail at loads of less than about 2,000 pounds per square inch. Theresins of this invention when adequately plasticized yield homogeneouscompositions which usually surpass the limits set forth.

For example, a composition was made which consisted of 70% by weight ofa polyvinyl partial acetal resin 62% acetalized with propionaldehyde,colloided with 30% by weight of triethylene glycol di(2-ethyl butyrate).At atmospheric temperatures this resin is insoluble in the plasticizernamed, but, by various expedients known in the art, the resin andplasticizer can be com.- bined to form clear and homogeneouscompositions.v The stress-strain characteristics of this compositionwere determined by subjecting specimens of it to increasing loads on atensile testing machine while observing the elongation as a function ofthe load applied. The samples of this composition tested at atmospherictemperature were found to have an 220% with an ultimate tensile strengthof about 3,700 pounds per square inch.

The stress-strain properties of another composition also containing 30%by weight of triethylene glycol di(2-ethyl butyrate) and 70% by weightof a polyvinyl acetal resin were determined in a parallel test underidentical conditions, but the resin in this case was more than 93%acetalized with propionaldehyde and was almost completely soluble in theplasticizer at ordinary temperatures. This composition possessed tensileproperties vastly different from that first discussed, and, although itselongation was around 300%, its ultimate tensile strength was less than300 pounds per square inch.

It is the elastic and tensile properties of the plasticized compositionsmade from the polyvinyl is allowed to elongation of about partial acetalresins of my invention which render the new resins so useful in themanufacture of non-shattering laminated glass, for coating fabricmaterials, and in many other uses, and which also distinguish these newresins from all of the known polyvinyl acetals and related classes ofvinyl resins.

-For example, resins of uniform quality result when a water solution ofthe polyvinyl alcohol is acidified with an inorganic acid substance,preferably a mineral acid, such as hydrochloric or sulfuric acid, andthe aldehyde added with constant stirring. Before any of the actualresin precipitate from the aqueous reaction mixture, an organic solventfor the resin which is miscible with water is added to maintain theresin in solution. Examples of such s01- vents are methanol, ethanol andisopropanol. By adding suitable amounts of the organic solvent(acidified if necessary) as the aldehyde is added, any desiredproportion of aldehyde and polyvinyl alcoholwithin the ranges set forthmay be reacted while the entire system is maintained as a single liquidphase.

An example of the conduct of the process according to the method justdescribed is given below for purposes of illustration:

44 parts by weight of polyvinyl alcohol (molecular weight about 6,000 to7,000) was dissolved in 200 parts by weight of water and 40 parts byweight of methyl alcohol and 36.8 parts by weight of sulfuric acid (sp.gr. 1.84) dissolved in additional methyl alcohol were added. To thissolution was added 87 parts by weight of propionaldehyde dissolved in anequal volume of methyl- .and thereafter the resin was precipitated fromthe reaction mixture by the addition of water.

The aqueous suspension of precipitated resin was made slightly alkalinewith sodium hydroxide and washed. Finally, it was redissolved, and thesolution was filtered. The resin was then precipitated and dried. Thisresin, on analysis, was found to be 62% acetalized.

The degrees of acetalization of the specific resins referred to abovewere calculated from the quantities of aldehyde inthe resins asdetermined by the following method:

A Z-gram sample of the dry resin is accurately weighedand placed in a500 cc. Erlenmeyer flask with cc. of normal butanol and 50 cc. of halfnormal hydroxylarnine hydrochloride solution. The sample is thenrefluxed for two hours in parallel with a blank. Thereafter, 50 cc. ofmethanol together with Mom phenol blue indicator is added and themixture titrated with half normal sodium hydroxide solution. From thedifference between the titrations of the sample and the blank there maybe calculated the amount of hydrochloric acid liberated from thehydroxylamine hydrochloride on the combination of hydroxylamine withaldehyde. From this .value the quantity of aldehyde present in theresin, or its degree of acetalization, may be calculated.

Modifications of the invention will be apparent to those skilled in theart. For example, if large variations are made in the amounts ofplasticizer to be incorporated with the resin or in the allowable waterabsorption or heat softening point of the resin, the composition of theresin may vary from those specifically set forth above. In addition, theresins may contain a limited proportion of ester, ketone, other aldehydeor functional groups normally foreign to the resinsof this invention,but in any case it is essential that such variations as are made in theresin composition, or the presence of such functional groups other thanfree hydroxyl and acetal groups of the aldehydes set forth within thelimits recited, must not be sufficient to affect the solubilityproperties which are characteristic of the new resins, primarilyythatability of the resin to form, with water-insoluble ester plasticizers,homogeneous compositions which are elastic and highly extensible whileretaining high ultimate strength. The polyvinyl partial acetal resinswhich are modified in non-material respects as indicated are includedwithin the scope of this invention, which should not be limited otherthan as defined by the appended claims.

This application is, in part, in continuation of and contains claims andsubject matter divided from my copending application Serial No. 236,556,filed October 22, 1938, which, in turn, is, in part, in continuation ofmy copending application Serial No. 741,997, filed August 29, 1934, andin continuation of my copending application Serial No. 115,476, flledDecember 12, 1936.

I claim:

1. A tough and strong artificial resin substantially identical with aresin resulting from the condensation of polyvinyl alcohol withsuflicient propionaldehyde to combine with from about 62% to about 88%of the hydroxyl groups of said polyvinyl alcohol, the total extent ofacetalization and the proportion of free hydroxyl groups in said resinbeing so correlated that said resin is substantially insoluble intriethylene glycol di(2- ethyl butyrate) plasticizer at ordinarytemperatures but is compatible with substantial quantities of saidplasticizer to form therewith flexible and elastic compositions whichhave at ordinary temperatures an elongation of at least about 200% andan ultimate strength above about 2,000

pounds per square inch.

2. A tough and strong artificial resin substantially identical with aresin resulting from the condensation of polyvinyl alcohol with aldehydematerial comprising propionaldehyde, the total extent of aldehydecombination in said resin and the proportion of free hydroxyl groupsthereof being so correlated that said resin is substantially insolublein triethylene glycol di(2 ethyl butyrate) plasticizer at ordinarytemperatures but is compatible with substantial quantities of saidplasticizer to form therewith flexible and' .triethylene glycoldi(2-ethyl butyrate) plasticizer ,while being virtually insoluble insaid plasticizer at ordinary temperatures.

4. A strong and resilient homogeneous composition of matter having anelongation of at least about 200% and an ultimate strength above about2,000 pounds per square inch at ordinary temperatures, which isessentially composed of a waterinsoluble ester plasticizer and apolyvinyl partial acetal resin substantially identical with a resinresulting from the condensation of polyvinyl alcohol with suflicientpropionaldehyde to combine With from about 62% to about 88% of thehydroxyl groups of said polyvinyl alcohol, the total extent ofacetalization and the proportion of free hydroxyl groups in said resinbeing so correlated that said resin is substantially insoluble in saidplasticizer at ordinary temperatures but is compatible with asubstantial quantity of said plasticizer to yield said homogeneouscomposition therewith.

5. A tough and strong composition of matter essentially composed of awater-insoluble ester plasticizer and a polyvinyl partial acetal resinacetalized with propionaldehyde between about 62% and about 88%, thedegree of acetalization with propionaldehyde and the proportion of freehydroxyl groups in said resin being so correlated that said resin isvirtually insoluble in said plasticizer at ordinary temperatures but iscompatible with substantial quantities of said plasticizer to yieldflexible and resilient homogeneous compositions therewith.

6. Process for making a polyvinyl partial acetal resin which comprisesforming a water solution of polyvinyl alcohol; adding to said solutionan inorganic acidic substance, propionaldehyde, and an'organic solventwhich in admixture with water is capable of dissolving said resin; theamount of propionaldehyde added being suflicient to react with fromabout 62% to about 88% of the hydroxyl groups of the polyvinyl alcoholpresent; and the rate at which said acidic substance, saidpropionaldehyde, and said organic solvent are added being such as tomaintain the whole in liquid phase.

HAROLD F. ROBERTSON.

